Capacitative high voltage pulse generating apparatus



May 30, 1967 E. BLANK 3,322,976

v CAPACITATIVE HIGH VOLTAGE PULSE GENERATING APPARATUS Filed March 51, I965 FIGZ INVENTOR EDWAR D BLAN K ATTORNEYS United States Patent 3,322,976 CAPACITATIVE HIGH VOLTAGE PULSE GENERATING APPARATUS Edward Blank, Sharon, Mass., assignor to Tobe Deutschmann Laboratories, Canton, Mass., a corporation of Massachusetts Filed Mar. 31, 1965, Ser. No. 444,160 6 Claims. (Cl. 307-109) The present invention relates in general to apparatus 7 for converting a low potential into a much higher potential and more particularly concerns novel capacitor apparatus in which the capacitor plates function as a transmission line to propogate a wave producing an output pulse of progressively increasing amplitude following shorting of an input terminal pair as the wave progresses toward an output terminal. A preferred embodiment of the invention includes means for storing additional energy to deliver an exceptionally high energy high potential pulse at the output terminal pair with high efficiency.

It is an object of this invention to provide means for storingenergy received at low potential and delivering this energy at much higher potential.

It is another object of this invention to achieve the preceding object with high efiiciency.

It is still another object of the invention to achieve the preceding objects with a relatively compact structure that is relatively easy and inexpensive to fabricate.

According to the invention, means define a plurality of adjacent transmission line portions. Means are provided for initially establishing an electric field in the transmission line portions to establish a series of electrostatic fields between output and common terminals with adjacent fields oppositely sensed, and means are provided for reversing the sense of alternate ones of the electrostatic fields so that all the electrostatic fields are arranged in series aiding relationship between the output and common terminals to develop a high potential therebe tween.

In the preferred form of the invention, the transmission line means comprises a common conducting strip insulatedly separated from a first conducting strip. These strips are coiled to form aspiral capacitor which may be charged by applying a relatively low potential between a first and common terminal respectively connected to the input end of the first and common strips and develop a high potential between an output terminal connected to the output end of the first conducting strip and the common terminal.

Still another feature of the invention resides in having a storage conducting strip insulatedly separated from the common strip and parallel to the first strip and connected to the first strip at the output end and to the output terminal for storing energy so that an exceptionally high energy high potential pulse may be provided between the output terminal and thecommon terminal.

Numerous other feature, objects and advantages of the invention will become apparentfrom the following specification when read in connection with the accompanying drawing in which:

FIG. 1 is a diagrammatic end view of a spiral capacitor according to the invention showing the arrangement of charging source and switching means.

FIG. 2 shows a preferred arrangement of the capacitor conducting foils and dielectric separators prior to being wound in a spiral, and

FIG. 3 is a perspective view of a typical capacitor according to the invention.

With reference now to the drawing and more particularly FIG. 1 thereof, there is shown a diagrammatic end view of a spiral capacitor with associated charging source and switching means arranged so that a high potential impulse may be delivered to the output terminal although the capacitor is charged from a relatively low potential source. The capacitor includes a common or grounded conducting strip 11 parallel to and insulatedly separated from another conducting strip 12 to define a first two conductor transmission line represented by the wavy line 13 and a second transmission line 14. A charging voltage source 15 is selectively connected to input terminal 16 by charging switch 21 to establish the potential E between input terminal 16 and common terminal 17 respectively connected to the ungrounded and grounded conducting strips 12 and 11, respectively. With charging switch 21 closed, ungrounded strip 12 assumes a potential of E with respect to grounded strip 11 to establish the upwardly oriented electric fields in transmission line 13 represented by the vectors 22 and 23 and the downwardly oriented electric field in transmission line 14 represented by the vector 14.

When the capacitor is fully charged with the vector oriented as indicated, the net electric field along the line defined by the vectors is essentially E/d where d is the separation between the first and common strip so that the potential between output terminal 26 and common terminal 17 is then essentially E. If now charging switch 21 is open and short circuiting switch 27 is closed, the orientation of vector 24 in transmission line 14 remains unchanged, but the orientation of vectors 22 and 23 reverse as the wave propagates along transmission line 13. The electric field along the line of vectors is then essentially approximately three times the magnitude of each of the vectors 22-24 prior to closing switch 27 to produce effectively a voltage impulse between terminals 26 and 17 approximatelythree times E/d.

For a theoretical analysis of relevant principles of operation reference is made to the paper of Fitch and Howell entitled Novel Principle of Transient High-Voltage Generation in 111 Proc. IEE 849 (April 1964), published after the invention disclosed and claimed in this application.

Referring to FIG. 2, there is shown a preferred arrangement of conducting foils and dielectric sheets prior to being rolled, incorporating the feature of storage capacitor means connected to the output terminal for providing a high energy output impulse. Common conducting foil 11 is sandwiched bet-ween a first pad of dielectric material 31 and a second pad 32. The first ungrounded conducting strip 12 and the second ungrounded conducting strip 33 (or charge conducting strip) are arranged parallel to one another and to common strip 11 and are sanwiched between the firstdielectric pad 31 and a third dielectric pad 34 (shown fragmentarily illustrated). The output ends of strips 12 and 33 are interconnected by a conducting link 35 with a tab at the output end of strip 12 comprising output terminal 26.

Referring to FIG. 3, there is shown the appearance of the capacitor thus formed when rolled up showing the high output terminal 26, the grounded input terminal 17 and the high input terminal 16. The location of the high terminal 26 near the axis is especially advantageous from the standpoint of maintaining as great a physical separation as practical between this high potential terminal and low potential points, such as a metallic case which may surround the capacitor and be at ground potential.

An important feature of the invention resides in having ungrounded charge strip 33 .coacting with the common strip 32 to define a charge storage capacitor so that when input terminals 16 and 17 are short circuited to initiate the generation of a high potential pulse at output high terminal 26, additional energy may flow from the storage capacitor for withdrawal from output terminal 26 to provide a pulse not only of exceptionally high potential, but also of high charge.

It is preferred that the capacitor according to the invention be made to establish the transit time of a circumferentially propagating wave per turn nearly the same. One way of accomplishing this result is by making the ratio of outer diameter to inner diameter slightly greater than one. A typical ratio in a practical embodiment is 7/6. It is also preferred that the foil thickness be of the order of ten times greater than normal foil thickness. Normal foil thickness in a high voltage capacitor is of the order of 0.25 mil while capacitors according to the invention incorporate conducting foils with a thickness of at least 2 mils, thereby providing effective field isolation between adjacent transmission line regions separated by a conducting foil and reducing 1 R (power) losses.

Without the charge storage capacitor comprising charge strip 33, at best only half the energy that initially charged the capacitor would be discharged from high output terminal 26. With the charge storage capacitor, as much as 90% of the energy initially charging the capacitor may be discharged from high output terminal 26.

Charge strip 33 is preferably wider than the first ungrounded conducting strip 12 having a width much greater than the thickness of the dielectric layers separating the ungrounded strips from the grounded strip 11. Charge strip 33 is preferably as wide as practical, for the improvement in efficiency is related to the ratio of charge storage capacity to the capacity between strips 11 and 12.

An exemplary 30 turn capacitor according to the invention with a capacity of the order of 0.25 microfarad may store approximately 28 joules of electrical energy when initially charged to 15 kilovolts and provide an output pulse of approximately 250 kilovolts in about A microsecond between output terminal 26 and common terminal 17 when input terminal 16 is connected to common terminal 17 at an energy efficiency of about 80% and a voltage multiplication efficiency of about 60%. Such a capacitor may have an inside diamter of about 2.0 inches, an outside diameter of about 3.5 inches, a length of about 8 inches, a charge storage strip 33 width of about 4 inches, an ungrounded strip 12 width of about one inch, a common strip 11 width of about six inches, conducting foils of 2 mil thick aluminum and dielectric insulating sheets each formed of sheets of 2 mil thick oil impregnated kraft paper.

It is evident that those skilled in the art may now make numerous modifications of and departures from the specific structures and techniques disclosed herein without departing from the inventive concepts. Consequently, the invention is to be construed as limited solely by the spirit and scope of the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Apparatus for converting a relatively low potential to a much higher potential comprising,

input, output and common terminals,

means defining a plurality of adjacent transmission line portions,

means for direct coupling said transmission line portions to said input and common terminals for initially establishing an electrostatic field in all said transmission line portions so that the electrostatic fields in adjacent transmission line portions are oppositely sensed and 4- vectorially combined between said common terminal and said output terminal, and means for selectively inverting the electrostatic field in alternate ones of said transmission line. portions to provide an impulse between said output and common terminals having a potential many times greater than the potential provided by the means for initially establishing said electrostatic field,

wherein said transmission line portions comprise a first conducting strip insulatedly separated from a common conducting strip to define a parallel plate capacitor,

said input and common terminals being respectively connected to said first strip and said common strip at the input end of said first and said common strips, said output terminal being connected to one of said first and common strips at the output end thereof, and further comprising, a storage conducting strip adjacent to and insulatedly separated from said common strip to define a storage capacity therebet-ween, and means interconnecting said first strip and said storage strip together only at the output ends thereof.

2. Apparatus in accordance with claim 1 wherein said transmission line portions comprise said conducting strips spiraled about acommon axis with said common strip separating adjacent transmission line portions to define two intertwined transmission lines.

3. Apparatus in accordance with claim 2 wherein the means defining the transmission line portions includes means establishing the transit time of an electromagnetic wave propagating about said common axis through said transmission line portions approximately the same for each revolution about said axis.

4. Apparatus in accordance with claim 3 wherein the ratio or the outer diameter to inner diameter of said spiraled conducting strips is slightly greater than one.

5. Apparatus in accordance with claim 2 wherein the thickness of said conducting strips is at least substantially 2 mils.

6. Apparatus in accordance with claim 2 wherein said means for initially establishing comprises a source of a low D.-C. potential,

and first switching means for selectively connecting said source of a low D.-C. potential to said input and common terminals,

and said means for selectively inverting comprises second switching means for seelctively connecting said input terminal to said common terminal.

References Cited FOREIGN PATENTS 11/1964 Great Britain.

OTHER REFERENCES April 1964, Fitch and Howell, Novel Principle of Transient High Voltage Generation, III, Proc. IEE 849. 

1. APPARATUS FOR CONVERTING A RELATIVELY LOW POTENTIAL TO A MUCH HIGHER POTENTIAL COMPRISING, INPUT, OUTPUT AND COMMON TERMINALS, MEANS DEFINING A PLURALITY OF ADJACENT TRANSMISSION LINE PORTIONS, MEANS FOR DIRECT COUPLING SAID TRANSMISSION LINE PORTIONS TO SAID INPUT AND COMMON TERMINALS FOR INITIALLY ESTABLISHING AN ELECTROSTATIC FIELD IN ALL SAID TRANSMISSION LINE PORTIONS SO THAT THE ELECTROSTATIC FIELDS IN ADJACENT TRANSMISSION LINE PORTIONS ARE OPPOSITELY SENSED AND VECTORIALLY COMBINED BETWEEN SAID COMMON TERMINAL AND SAID OUTPUT TERMINAL, AND MEANS FOR SELECTIVELY INVERTING THE ELECTROSTATIC FIELD IN ALTERNATE ONES OF SAID TRANSMISSION LINE PORTIONS TO PROVIDE AN IMPULSE BETWEEN SAID OUTPUT AND COMMON TERMINALS HAVING A POTENTIAL MANY TIMES GREATER THAN THE POTENTIAL PROVIDED BY THE MEANS FOR INITIALLY ESTABLISHING SAID ELECTROSTATIC FIELD, WHEREIN SAID TRANSMISSION LINE PORTIONS COMPRISE A FIRST CONDUCTING STRIP INSULATEDLY SEPARATED FROM A COMMON CONDUCTING STRIP TO DEFINE A PARALLEL PLATE CAPACITOR, SAID INPUT AND COMMON TERMINALS BEING RESPECTIVELY CONNECTED TO SAID FIRST STRIP AND SAID COMMON STRIP AT THE INPUT END OF SAID FIRST AND SAID COMMON STRIPS, SAID OUTPUT TERMINAL BEING CONNECTED TO ONE OF SAID FIRST AND COMMON STRIPS AT THE OUTPUT END THEREOF, AND FURTHER COMPRISING, A STORAGE CONDUCTING STRIP ADJACENT TO AND INSULATEDLY SEPARATED FROM SAID COMMOM STRIP TO DEFINE A STORAGE CAPACITY THEREBETWEEN, AND MEANS INTERCONNECTING SAID FIRST STRIP AND SAID STORAGE STRIP TOGETHER ONLY AT THE OUTPUT ENDS THEREOF. 